The short answer
Partial response, stable disease and progression are measurement categories from a scan rulebook called RECIST. Stable disease means the tumors changed less than the rulebook thresholds.
These terms measure tumor size on scans using a standard rulebook (RECIST 1.1), not how well you are doing overall.
Under RECIST, partial response means the sum of the measured tumor diameters has fallen by at least 30% from baseline.
Progressive disease means a rise of at least 20% from the smallest sum recorded, with a minimum absolute increase of 5 mm, or any new lesion.
Stable disease is everything in between — a tumor that shrank 25% and one that grew 15% both fall into it.
On this page
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The whole article, with every detail and caution.
This page is for people reading a scan report that says "partial response" or "stable disease." It explains what these labels measure, how they are worked out, and what to ask your care team.
What these words are measuring
Partial response and stable disease do not describe how you are doing. They are measurements of tumor size on scans. Doctors use a standard rulebook so results mean the same thing in different hospitals and trials. For solid tumors, that rulebook is usually RECIST (Response Evaluation Criteria in Solid Tumors), currently version 1.1.
These are measurement categories. They are not grades, verdicts, or predictions. Knowing that can take a lot of weight off them.
The baseline scan
Before treatment starts, a radiologist (a doctor who reads scans) picks a small number of tumors that can be measured. These are called target lesions. The radiologist measures the longest width of each one. Those measurements are added into a single number, called the sum of diameters. That sum is the baseline.
Every later scan measures the same lesions and gives a new sum.
- Response is judged against the baseline.
- Progression (growth) is judged against the smallest sum recorded so far, called the nadir, once the tumor has shrunk.
This is why the same lesion size can be described differently at different times. It is also why comparing your latest scan only with your previous one can mislead.
The four categories in plain words
- Complete response: all target lesions have disappeared.
- Partial response: the sum of diameters has fallen by at least 30% from baseline.
- Progressive disease: the sum has risen by at least 20% from the smallest it has been, and by at least 5 mm in absolute terms. A new lesion appearing anywhere also counts.
- Stable disease: neither of the above. There is not enough shrinkage to call a partial response and not enough growth to call progression.
The 5 mm rule exists for a good reason. Measurement is not perfectly precise. A 20% change in a small lesion can be a couple of millimeters. That is well within the normal variation between radiologists, scanners, and how you were breathing during the scan. The minimum size change stops this "noise" from being reported as progression.
Notice how wide stable disease is. A tumor that shrank 25% is stable disease. One that grew 15% is also stable disease.
What stable disease does and does not mean
This is the most common misreading of these reports. Stable disease only means the tumors did not shrink or grow enough to cross the RECIST thresholds. It is not the same as the cancer growing. What it means for you depends on your cancer and treatment, so ask your care team.
Shrinking a tumor and helping a patient are not the same thing, and a scan label is only one piece of the picture. Your team decides next steps from the whole picture.
Where the categories get blurry
- Some disease can't be measured. Examples are bone metastases (cancer that has spread to bone), a thin layer of tumor, or fluid in the abdomen. These are tracked as non-target disease and described in words rather than numbers.
- Some treatments can be hard to judge on scans. Your team may repeat a scan rather than act on a single result. Ask how your treatment is judged.
- Radiologists differ. They may choose slightly different lesions or judge edges differently. Small changes between reports are common and often mean nothing.
- Blood tests and scans don't always agree. Tumor markers in the blood do not always move in step with the scans. Neither one alone is the whole picture.
- RECIST is a measuring rulebook. It is not a verdict on one person. Your oncologist reads it alongside your symptoms, exam, and blood tests.
What to ask when you get a result
- What was my scan compared against?
- By how many millimeters did things actually change, not just which label was used?
- Is the change within the range of normal measurement variation?
- Does the plan change because of this result? If not, what would need to happen for it to change?
- What does "stable" mean in my situation?
Ask your team what "stable" means in your situation.
Sources
- RECIST 1.1 thresholds (30%, 20%, 5 mm) come from the published guideline: Revised RECIST guideline version 1.1 (full text PDF)
Common questions
My scan says stable disease. Is the treatment working?
It can be. Stable disease means the tumor has neither shrunk enough to count as a response nor grown enough to count as progression. Whether it is the result your team hoped for depends on your cancer and your treatment, so ask them what stable means for you.
Why does a few millimetres of growth not count as progression?
Because measurement is not perfectly precise. A 20% change in a small lesion can be one or two millimetres, which is within normal variation between radiologists, scanners and how you were breathing. The rule requires both a 20% relative increase and at least 5 mm absolute, so that noise is not reported as progression.
My last scan was compared to something different. Why?
Response is judged against the original baseline, and progression against the smallest sum recorded during treatment (the nadir). This is deliberate: it stops a tumor that shrank a lot and then regrew slightly from being scored as a continuing response.
What if my tumors grew at first on immunotherapy?
Your team may repeat a scan rather than act on a single result, because scan changes can be hard to read. Ask them how immunotherapy is judged on scans.
Why doesn't my tumor marker match my scan?
Blood markers and imaging measure different things and do not always move together. Neither on its own is the whole picture, and your team interprets them alongside how you feel and your examination.
Questions to ask your doctor
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Written by: Cancer ExplainedSources last checked: 2026-10-02 what this meansLast updated: 2026-10-02Next planned review: 2027-07-30
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Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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